Electrician{40 s knife

ABSTRACT

An electrician&#39;&#39;s knife usable for wiring is disclosed in which the handle portion thereof comprises an integral thick insulation and a substantially flat tube which serves as a sheath for receiving a cutting blade adapted to be axially slidable therein but inseparable therefrom. The cutting blade is easily pulled out of the sheath by the fingers, but once pulled out, it is held stable by means of a pair of support pins and a stopper projection formed on a plate spring unless a pressing force is applied thereto.

Uitd tates Patent Nagaltt 1 Sept. a, T973 [54] ELMTRICIAN S KNIFEFOREIGN PATENTS OR APPLlCATlONS l l Inventor: Kaisuyuki Nagaki, 26-14310649,406 1/1951 Great Britain 30/162 Noenakano-cho, Joto-ku, Osaka, JapanPrimary Examiner-Othell M. Simpson [22] Filed: Oct. 4, 1971 AssistantExaminer-Gary L. Smith Attorney-Alvin Browdy [2]] Appl. No.: 186,282

57] ABSTRACT l l Foreign Application Priority Data An electricians knifeusable for wiring is disclosed in Feb. 27. l97l Japan 46/12520 (utilitymodel) which the handle portion thereof comprises an integral thickinsulation and a Substantially flat tube which [52] U.S. Cl. 30/154serves as a sheath for receiving a cutting blade adapted [51 Int. Cl1326b 3/06 o be xi lly lidable therein bu inseparable therefrom. [58]Field of Search 30/154, 162; The cutting blade is easily pulled out ofthe sheath by 145/50 C, 64 the fingers, but once pulled out, it is heldStable by means ofa pair of Support pins and a Stopper projection [56]References Cited formed on a plate spring unless a pressing force is ap-UNITED STATES PATENTS Crum 30/ 162 plied thereto.

7 Claims, 4 Drawing Figures I ELECTRICIANS KNIFE The present inventionrelates generally to a cutting instrument for use in electric wiredistributing work, and more particularly to such a sheath typeelectricians knife that is mainly usable for stripping insulation fromelectric wires and cables or cutting them. The knife comprises a handleportion including a thick insulation for protecting the user fromelectric shock and a substantially flat metallic tube which serves as asheath for storing the cutting blade which is adapted to be axiallyslidable therein but inseparable therefrom. The cutting blade can beeasily pulled out in the axial direction of the sheath by fingers, butonce pulled out it is held stable by means of a pair of support pins anda stopper projection formed on a plate spring unless a pressing force isgiven thereto.

Conventionally, most of the cutting instruments employed to stripinsulation from electric wires and cables or cut them are clasp typeknives according to which a cutting blade, when not in use, is pivotallysupported with a hinge mounted adjacent one end of a slotted handle. Onthe other hand, the sheath type knives are rarely used in the field forthe reasons to be described hereinafter.

When the above-mentioned conventional clasp type knife is employed,there is a fatal defect in that the cutting blade is accompanied by ajeopardy that a user will occasionally hurt himself because the cuttingblade is liable to unexpectedly pivot back into the slotted handle.

Further, in such a clasp type knife, the handle portion must be providedlongitudinally at one side with a slot for receiving the cutting blade;consequently, the ten dency is generally evident that undesired electroconductive foreign matters produced during the operation and themoisture existing around a labor site are easily allowed to come inthrough said slot thereby forming an unexpected electrical connectioncausing dreadful electric shock.

Meanwhile, the conventional sheath type electricians knives are rarelyused in the field since they generally comprise a haft portion, a bladeportion rigidly embedded or secured to said haft portion, and a sheathportion independently separable from said blade portion so that thesheath portion which, when in use, is generally separated from theunsheathed blade portion often gets lost.

Accordingly, the present invention aims at eliminating all theabove-mentioned defects by providing a novel and useful electriciansknife that comprises a handle portion including a substantially flattube servable as a sheath for slidably receiving a blade, and a thickinsulation covering said sheath so that even if an electrician happensto work at a hot line charged with high voltage, he is safely protectedagainst electric shock.

Another object of the invention is to provide an improved sheath typeelectrician s knife in which the foremost end of the cutting blade isthick and round, having a hole bored therethrough through or a pair ofconcavities formed therein making it possible for an electrician toeasily pull the cutting blade out of the sheath with his fingers engagedin said hole or concavities.

A still further object of the invention is to provide an improved sheathtype electrician s knife having a nonslip head provided adjacent theround corner of the foremost end of the blade so that an electrician caneasily push back the cutting blade into the sheath by pressing saidnon-slip head against a surface of any hard object accessible to him.

A yet further object of the invention is to provide an improved sheathtype electrician s knife wherein stability of the pulled-out cuttingblade is insured by a pair of support pins and a stopper projectionformed on a plate spring for engaging with a recess formed in the backedge of the blade.

These and other objects and advantages of the present invention willbecome more apparent from the following description made with referenceto a preferred embodiment of the invention shown by way of example inthe accompanying drawing and the appended claims.

In the drawing:

FIG. 1 is a perspective view of .an electricians knife in accordancewith the present invention, wherein the cutting blade is shown with itsfull length pulled out of the sheath;

FIG. 2 is an elevational view taken partly in section of the knife ofFIG. 1, showing in phantom lines the positional relation assumed by thecutting blade when the non-slip head formed on the foremost end of thecutting blade is forcibly pressed;

FIG. 3 is likewise an elevation taken partly in section of the knife ofFIG. 1, with the cutting blade fully sheathed; and

FIG. 4 illustrates in detail the elemental parts of the engagingmechanism formed with a stopper projection and a recess in the back edgeof the blade.

Referring now to the drawing, the electricians knife in accordance withthe present invention comprises a handle portion generally designated byreference character A which includes a substantially flat metallic tube10 servable as a sheath for slidably storing a cutting blade generallydesignated by reference character B and a thick insulation 11 coveringsaid tube or sheath l0.

Said sheath has a pair of opposed narrow walls 10a, 10a, a pair ofopposed comparatively broad walls 10b, 10b, and a bottom wall 10c. Alongthe inner surface of said narrow wall there is provided a plate spring12 which extends slopewise slightly upwardly away from said bottom wall100 and is secured at one end to said wall 10a adjacent the bottom wallWe by snapping its foremost bent portion 12a into a small slit (notshown in the drawing) provided in the wall 100 so that the back 18 ofthe cutting blade B is normally kept in an upwardly pressed state by theplate spring 12 as shown in FIGS. 2 and 3. In this connection, it willeasily be understood that said bottom wall 100 may be omitted.

One end of said back edge 18 is notched with a recess or valley 14having a configuration corresponding to an integrally formed projection13 on the plate spring 12. Thus, when the cutting blade 10 is slidablypulled out of the sheath, said projection 13 is naturally brought intointerlocked engagement with said recess or valley 14 thereby controllingthe axial movement of the cutting blade 10 as is particularly shown inFIG. 2. In addition, the cutting blade B thus pulled out of the sheath10 can be completely prevented from, the undesired counter-clockwiseswinging movement, which otherwise may give rise to an excessivedecrease of the cutting effect of the blade B, by means of a pair ofsupport pins 15, 16 rigidly fixed in opposed relation with each otheradjacent the opening end of the sheath W, with the outer pin 16 fixedopposite the blade back edge 18 and the inner pin 15 opposite thecutting edge 19. To be more precise, even if a pressing force or cuttingresistance is applied to the cutting edge 19 to urge the blade B to turncounterclockwise about said outer pin 16, said inner pin 15 serves tokeep the blade B unmoved thus securing the stability of the cuttingblade B through the full course of the cutting operation.

In contrast thereto, when a pressing force is applied to the back edge18 in the direction shown by an arrow in FIG. 2, the cutting blade B isurged to move about the inner pin 15 in said direction or the clockwisedirection while at the same time the plate spring 12 is presseddownwardly by the rearmost end of the back edge 18 until it reaches theparticular position shown in FIG. 4, wherein the stopper projection 13of the plate spring 12 is caused to go out of the recess 14 of the backedge 18 with the result that the cutting blade B is completely releasedfrom the engaged relation with the plate spring 12 and is permitted toslide back into the sheath 10. Therefore, the cutting blade B can bestored back into the sheath 10, merely by pushing the blade B in theaxial direction, with said stopper projection 13 disconnected from therecess 14 as is shown in FIG. 4.

The sheath has its outer surface covered with a comparatively thickinsulation 11 preferably made from a non-conductive synthetic resin withthe exception of its opening end portion whereby a user is safelyprotected against possible electric shock even when working at a hotline.

Incidentally, a hole 17 may be provided at one end of the insulation soas to suspend the knife on a users belt by passing a string on the beltthrough hole 17.

In the present embodiment, the foremost end of the cutting blade B isprovided with a hole 20 so as to help a user pull out the blade B fromthe sheath 10 with the hole 20 between his finger tips. However, it isalso possible to secure this pulling effect by replacing said hole 20with a concavity or indentation (not shown) that will serve as a fingerslip preventing means.

Further, said foremost end of the cutting blade B is preferably formedinto a semi-circular shape having a non-slip head 21 provided with aplurality of notches or indentation 22 by means of which said head 21 iseffectively pressed against a surface of any hard object accessible tohim in order to disengage the stopper projection 13 out of the recess 14formed in the blade B.

Preferably the cutting blade B is inwardly curved along its edge 19 asillustrated in FIGS. 1 to 4 inclusive so that the cutting edge 19 iskept out of touch with the inner support pin in the course of the axialmovement thereof, consequently obviating a fear that the edge 19 maybecome dulled.

As has been understood from the above description, the present inventionprovides a simple and inexpensive electricians knife characterized inthat the sheath portion is covered with a thick insulation and thecutting blade is slidable longitudinally thereof within the sheathportion, thus always protecting a user from electric shock andpreventing him from hurting himself.

Although one form of the invention has been shown and describedhereinabove by way of illustration, it will be understood that theinvention is not to be limited to the exact construction shown anddescribed, but that various changes and modifications may be madewithout departing from the spirit and scope of the invention, as definedin the appended claims.

I claim:

1. An electricians knife, comprising:

a handle including a substantially flat tube, open at one end, servableas a sheath, and an external insulation covering said sheath;

a cutting blade, having a cutting edge, a back edge, a foremost end anda rearmost end, axially slidable within said sheath but inseparabletherefrom;

an outer support pin fixedly secured adjacent the open end of saidsheath on the inside thereof opposite the back edge of said cuttingblade;

an inner support pin fixedly secured adjacent the open end of saidsheath on the inside thereof opposite the cutting edge of said cuttingblade;

said inner support pin being located relatively inwardly within saidsheath with respect to said outer support pin so that when in operationsaid cutting blade is prevented from swinging about said outer supportpin;

plate spring extending gradually upward in the direction of said openend of said sheath along the inner wall of said sheath opposite the backedge of said blade, said plate spring having one end fixedly secured tosaid sheath;

a stopper projection formed at the end of said plate spring adjacent theopen end of said sheath and kept in abutment with the back edge of saidcutting blade under the upward pressure of said plate spring;

a recess means formed on the back edge of said cutting blade forreleasably engaging said stopper projection; and

said cutting blade having its one end supported on said inner supportpin against the resiliency of said plate spring when said recess meansis engaged with said stopper projection so as to be slightly swingableabout said inner support pin thereby to release the interlockedengagement of said stopper projection with said recess means.

2. The electricians knife, as set forth in claim 1,

wherein said external insulation is made of nonconductive syntheticmaterial.

3. The electricians knife, as set forth in claim 1,

wherein said sheath is made of metal.

4. The electricians knife, as set forth in claim 1,

wherein the cutting edge of said cutting blade has an inwardly curvedsurface.

5. The electricians knife, as set forth in claim 1,

wherein the foremost end of said cutting blade is substantially roundand provided with a plurality of notches.

6. The electricians knife, as set forth in claim 1,

wherein said cutting blade has a finger slip preventing means at theforemost end thereof.

7. The electricians knife, as set forth in claim 6,

wherein said finger slip preventing means is in the form of a hole boredthrough said foremost end of said cutting blade.

Patent No. 3755893 Dated p mber 4, 1973 Inventor s Ka'tsuyuki NAGAKI Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 44, delete "slopewise'h Signed and sealed this 12th dayof February 1974 (SEAL) Attest:

EDWARD M.FLET( JHER,JR, Co MARSHALL DANN Attesting OfflCeT Commissionerof Patents F ORM PO-1050 (10-69] USCOMM-DC 60376-P69 UVS. GOVERNMENTPRINTING OFFICE: I959 O--386-3J4

1. An electrician''s knife, comprising: a handle including asubstantially flat tube, open at one end, servable as a sheath, and anexternal insulation covering said sheath; a cutting blade, having acutting edge, a back edge, a foremost end and a rearmost end, axiallyslidable within said sheath but inseparable therefrom; an outer supportpin fixedly secured adjacent the open end of said sheath on the insidethereof opposite the back edge of said cutting blade; an inner supportpin fixedly secured adjacent the open end of said sheath on the insidethereof opposite the cutting edge of said cutting blade; said innersupport pin being located relatively inwardly within said sheath withrespect to said outer support pin so that when in operation said cuttingblade is prevented from swinging about said outer support pin; a platespring extending gradually upward in the direction of said open end ofsaid sheath along the inner wall of said sheath opposite the back edgeof said blade, said plate spring having one end fixedly secured to saidsheath; a stopper projection formed at the end of said plate springadjacent the open end of said sheath and kept in abutment with the backedge of said cutting blade under the upward pressure of said platespring; a recess means formed on the back edge of said cutting blade forreleasably engaging said stopper projection; and said cutting bladehaving its one end supported on said inner support pin against theresiliency of said plate spring when said recess means is engaged withsaid stopper projection so as to be slightly swingable about said innersupport pin thereby to release the interlocked engagement of saidstopper projection with said recess means.
 2. The electrician''s knife,as set forth in claim 1, wherein said external insulation is made ofnonconductive synthetic material.
 3. The electrician''s knife, as setforth in claim 1, wherein said sheath is made of metal.
 4. Theelectrician''s knife, as set forth in claim 1, wherein the cutting edgeof said cutting blade has an inwardly curved surface.
 5. Theelectrician''s knife, as set forth in claim 1, wherein the foremost endof said cutting blade is substantially round and provided with aplurality of notches.
 6. The electrician''s knife, as set forth in claim1, wherein said cutting blade has a finger slip preventing means at theforemost end thereof.
 7. The electrician''s knife, as set forth in claim6, wherein said finger slip preventing means is in the form of a holebored through said foremost end of said cutting blade.